This invention relates to a supercharging apparatus for an internal combustion engine. More specifically, this invention relates to such a supercharging apparatus in which intake air for to the engine is compressed on its way from an inlet of an air intake system to an outlet thereof.
A variety of superchargers are generally used for internal combustion engines. In recent years, screw type superchargers have been used because they enhance of the volumetric efficiency and the possibility of improving overall adiabatic efficiency. In a case where such a type of supercharger is arranged in an air intake system of an engine and is used for compressing the intake air, it is necessary to relieve or reduce the pumping loss of the supercharger because the supercharger causes a relatively large pumping loss at low or partial load operating conditions of the engine.
Conventionally, under these circumstances, the supercharger is connected to drive means for the supercharger through an electromagnetic clutch, and the clutch is released when the supercharging effect is not required, so that the supercharger is not being driven. This kind of supercharger, however, has relatively large resistance to running during its non-driven state and is difficult to idle. Therefore, a torque shock due to an engagement of the electromagnetic clutch occurs as the clutch is changed from its disengagement to engagement states. To prevent such a torque shock, it is required to engage the clutch in a relatively low engine speed zone, even if the engine is not required to be supercharged in a low load operating condition. It follows that it is desirable to deactivate the compression action of the supercharger entirely, or to greatly relieve the compression action. If the compression action of the supercharger can be deactivated entirely or relieved greatly, advantages would be obtained. For instance, the torque shock due to the engagement of the electromagnetic clutch could be depressed and, therefore, the rotating speed engaging the clutch in the low load operating condition could be enhanced. This is brought about because the supercharger can idle during its non-driven state, and the significant differences between the rotating speed thereof and the rotating speed of the drive means for the supercharger are thus avoided.
In Japanese Laid-Open Publication No. 63-170524, it has been proposed to make a supercharging apparatus for an internal combustion engine having both a screw type supercharger and a turbocharger such that the capacity of the screw type supercharger is reduced to decrease the pumping loss when the engine is operated in partial load conditions. That is, in this conventional supercharging apparatus, the screw type supercharger has control valves which are slideable axially, and its intake air inlet is adapted to be opened by the control valves in order to reduce the capacity of the supercharger.
This type of supercharger might be able to reduce the pumping loss in low load or partial load operating conditions to some extent. However the compression action thereof still remains, and therefore, since the idle rotation of the supercharger is limited during its disengagement with the drive means, the torque shock occurs upon an engagement with the drive means for the supercharger owing to a considerable variation in the engine torque.